An improved method and apparatus is provided for use in the casting of reactive metals.
During a known casting process, molten metal is poured into a mold and then solidified. If the molten metal contains reactive elements, the reactive elements are depleted by both their reactivity and by vaporization. The depletion of the reactive elements may result in the cast articles having properties which are not satisfactory for the intended use of the articles.
During the casting of single crystal articles, the molten metal in a mold is solidified in a uni-directional manner. In order to effect the uni-directional solidification of the molten metal, the metal remains molten for a relatively long time as the mold is withdrawn from a furnace chamber. The relatively long solidification time enables reactive elements to migrate to the surface of the molten metal and to be vaporized. As the reactive elements migrate from an article mold cavity, the chemistry of the alloy is changed in a manner which can be detrimental to the properties of the cast article.